Signaling aliasing capability in data centers

ABSTRACT

Techniques are described for signaling aliasing capability between routers in a multi-tenant data center that uses VPNs, such as Ethernet VPNs. In the multi-tenant data center, two or more PE routers may be connected to a CE router by a multi-homed L2 segment in an all-active mode. Aliasing refers to the ability of a PE router to signal that it can reach a given multi-homed L2 segment even when the PE router has learned no MAC addresses over that multi-homed L2 segment. The PE routers on the multi-homed L2 segment advertise aliasing capability using a route advertisement on a per-L2 segment basis. When the multi-tenant data center uses global VPN identifiers, no additional information is needed by a remote PE to build an ECMP next hop to the PE routers that support aliasing, and transmission of a route advertisement on a per-VPN basis may be suppressed.

This application claims the benefit of India Patent Application No.5642/CHE/2014, filed Nov. 10, 2014, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The invention relates to computer networks and, more specifically, toforwarding multicast traffic within data centers.

BACKGROUND

A data center is a specialized facility that provides data serving andbackup as well as other network-based services for subscribers and otherentities. A data center in its most simple form may consist of a singlefacility that hosts all of the infrastructure equipment, such asnetworking and storage systems, servers, redundant power supplies, andenvironmental controls.

More sophisticated data centers may be provisioned for geographicallydispersed organizations using subscriber support equipment located invarious physical hosting facilities (i.e., sites). In some cases, eachof these sites may include switches, servers, storage area networks(SANs) or other equipment configured to operate as one portion of asingle data center. In other cases, each of these sites may beconfigured to operate as a single data center itself. In either case,techniques have been developed to connect two more of the sites to forma single, logical multi-tenant data center. For example, a multi-tenantdata center may be formed using Ethernet virtual private networks(EVPNs) as Network Virtualization Overlay (NVO) instances over anInternet Protocol (IP) underlay network. This may be especially usefulin cases were the multi-tenant data center includes virtual hosts, e.g.,virtual machines (VMs).

SUMMARY

In general, techniques are described for signaling aliasing capabilitybetween routers in a multi-tenant data center that uses layer two (L2)virtual private networks (VPNs), such as Ethernet Virtual PrivateNetworks (EVPNs). In the multi-tenant data center, two or more provideredge (PE) routers may be connected to a customer edge (CE) router by amulti-homed L2 network segment, e.g., a multi-homed Ethernet segment(ES), in an all-active mode. In this arrangement, less than all of thePE routers on the multi-homed L2 network segment may, in some cases,learn a set of L2 addresses, e.g., media access control (MAC) addresses,associated with the CE router. In such situations, each of the PErouters that did not learn the set of MAC addresses associated with theCE router may nevertheless signal that it can reach a given multi-homedL2 network segment, referred to as “aliasing,” with respect to the L2addresses. According to the techniques of this disclosure, the PErouters on the multi-homed L2 network segment utilize an enhancedrouting protocol that allows the PE routers to signal aliasingcapability on an L2 network segment basis (e.g., per ES). In addition,in some examples in which a global VPN identifier is used, each of thePE routers on the multi-homed L2 network segment may suppresstransmission of an additional route advertisement on a per-VPN basis(e.g., per-EVI).

As an example, the PE routers of a multi-homed ES may, according to thetechniques described herein, advertise aliasing capability using aper-ES auto-discovery (AD) route advertisement that includes an EthernetSegment Identifier (ESI) Label Extended Community with an aliasing bit.In cases where the multi-tenant data center uses globally unique VirtualNetwork Identifiers (VNIs) for EVPN instances (EVIs), no additionalinformation is needed by a remote PE to build an equal-cost multi-path(ECMP) next hop to the PE routers on the multi-homed ES that supportaliasing, and transmission of a per-EVI route advertisement may besuppressed.

In one example, this disclosure is directed to a method comprisingestablishing, between a first site and a second site of a multi-tenantdata center, an Ethernet virtual private network (EVPN) including two ormore provider edge (PE) routers connected to a customer edge (CE) routerof the first site on a multi-homed Ethernet segment (ES) in anall-active mode, and at least one remote PE router; receiving, by afirst PE router of the two or more PE routers on the multi-homed ES fromthe CE router, a packet with a media access control (MAC) addressassociated with the CE router; sending, by the first PE router to the atleast one remote PE router, a MAC route advertisement including the MACaddress associated with the CE router; and sending, by at least a secondPE router of the two or more PE routers on the multi-homed ES to the atleast one remote PE router, a per-ES auto-discovery (AD) routeadvertisement indicating whether the second PE router supports aliasingfor the multi-homed ES.

In another example, this disclosure is directed to a system comprisingtwo or more provider edge (PE) routers included in an Ethernet virtualprivate network (EVPN) established between a first site and a secondsite of a multi-tenant data center, the two or more PE routers connectedto a customer edge (CE) router of the first site on a multi-homedEthernet segment (ES) in an all-active mode; a first PE router of thetwo or more PE routers on the multi-homed ES configured to receive, fromthe CE router, a packet with a media access control (MAC) addressassociated with the CE router, and send, to at least one remote PErouter included in the EVPN, a MAC route advertisement including the MACaddress associated with the CE router; and a second PE router of the twoor more PE routers on the multi-homed ES configured to send, to the atleast one remote PE router, a per-ES auto-discovery (AD) routeadvertisement indicating whether the second PE router supports aliasingfor the multi-homed ES.

In a further example, this disclosure is directed to a method comprisingestablishing, between a first site and a second site of a multi-tenantdata center, an Ethernet virtual private network (EVPN) including two ormore provider edge (PE) routers connected to a customer edge (CE) routerof the first site on a multi-homed Ethernet segment (ES) in anall-active mode, and at least one remote PE router; receiving, by theremote PE router from a first PE router of the two or more PE routers onthe multi-homed ES, a media access control (MAC) route advertisementincluding a MAC address associated with the CE router; receiving, by theremote PE router from at least a second PE router of the two or more PErouters on the multi-homed ES, a per-ES auto-discovery (AD) routeadvertisement indicating whether the second PE router supports aliasingfor the multi-homed ES; and based on the per-ES AD route advertisementindicating that the second PE router supports aliasing for themulti-homed ES, building, by the remote PE router, an equal-costmulti-path (ECMP) next hop to at least the first and second PE routerson the multi-homed ES to reach the MAC address associated with the CErouter over the multi-homed ES.

In an additional example, this disclosure is directed to a routercomprising a routing engine configured to establish an Ethernet virtualprivate network (EVPN) between a first site and a second site of amulti-tenant data center, the EVPN including two or more provider edge(PE) routers connected to a customer edge (CE) router of the first siteon a multi-homed Ethernet segment (ES) in an all-active mode, whereinthe router is a remote PE router included in the EVPN, receive, from afirst PE router of the two or more PE routers on the multi-homed ES, amedia access control (MAC) route advertisement including a MAC addressassociated with the CE router, receive, from at least a second PE routerof the two or more PE routers on the multi-homed ES, a per-ESauto-discovery (AD) route advertisement indicating whether the second PErouter supports aliasing for the multi-homed ES, and based on the per-ESAD route advertisement indicating that the second PE supports aliasingfor the multi-homed ES, build an equal-cost multi-path (ECMP) next hopto at least the first and second PE routers on the multi-homed ES toreach the MAC address associated with the CE router over the multi-homedES. The router further comprises a forwarding engine configured toforward data packets destined for the MAC address associated with the CErouter according to the ECMP next hop.

In another example, this disclosure is directed to a method comprisingestablishing, between a first site and a second site of a multi-tenantdata center, a layer two virtual private network (L2 VPN) between two ormore provider edge (PE) routers and at least one remote PE router,wherein the two or more PE routers are connected to a customer edge (CE)router of the first site by a multi-homed L2 network segment associatedwith a particular customer, and wherein the two or more PE routers areconfigured to operate in an all-active mode in which all of the PErouters forward L2 traffic from the at least one remote PE to the CErouter over the multi-homed L2 network segment; receiving, by a first PErouter of the two or more PE routers and from the CE router, a packetwith an L2 address associated with the CE router; sending, by the firstPE router to the at least one remote PE router, a route advertisementincluding the L2 address associated with the CE router; and sending, byat least a second PE router of the two or more PE routers to the atleast one remote PE router using a routing protocol, an auto-discovery(AD) route advertisement associated with the multi-homed L2 networksegment indicating whether the second PE router supports aliasing forthe multi-homed L2 network segment to reach the L2 address associatedwith the CE router without having learned the L2 address over themulti-homed L2 network segment.

The details of one or more examples of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example multi-tenant datacenter using Ethernet virtual private network (EVPNs) in which provideredge (PE) routers on multi-homed Ethernet segments (ESs) signal aliasingcapability according to the techniques of this disclosure.

FIG. 2 is a conceptual diagram illustrating an example of an EthernetSegment Identifier (ESI) Label Extended Community included with a per-ESauto-discovery (AD) route advertisement, in accordance with thetechniques of this disclosure.

FIG. 3 is a block diagram illustrating an example router capable ofperforming the disclosed techniques.

FIG. 4 is a flowchart illustrating an example operation of PE routers ona multi-homed ES signaling aliasing capability to a remote PE in amulti-tenant data center using EVPNs.

FIG. 5 is a flowchart illustrating an example operation of a remote PErouter receiving aliasing capability signaling from PE routers on amulti-homed ES in a multi-tenant data center using EVPNs.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating an example multi-tenant datacenter 2 using Ethernet virtual private network (EVPNs) in whichprovider edge (PE) routers on multi-homed Ethernet segments (ESs) signalaliasing capability according to the techniques of this disclosure. Inthe example of FIG. 1, data center sites 5A-5B (collectively, “sites 5”)may each operate as a single data center itself or may each operate as aportion of a single data center. In either case, sites 5 are connectedtogether to form single, logical multi-tenant data center 2. In otherexamples, a multi-tenant data center may include more than two sites.

Each of sites 5 are networks having specialized facilities that providestorage, management, and dissemination of data to subscribers and otherentities. In the illustrated example of FIG. 1, each of sites 5A, 5Bincludes a plurality of servers 9A, 9B and storage area networks (SANs)14A, 14B respectively that provide computing environments forsubscribers/customers. Subscriber devices (not shown) may connect tosites 5 to request and receive services and data provided by sites 5 andmulti-tenant data center 2 as a whole. In some instances, sites 5A, 5Bmay provide geographical redundancy against localized failure of onesite of multi-tenant data center 2.

In the example of FIG. 1, sites 5 are interconnected by an EVPN 23 as aNetwork Virtualization Overlay (NVO) instance over an Internet Protocol(IP) underlay network 4. This configuration may be especially useful incases were sites 5 of multi-tenant data center 2 include virtual hosts,e.g., virtual machines (VMs). In general, IP underlay network 4represents a layer three (L3) network and may include multipleintermediate routing and switching devices (not shown) that transportdata traffic over links between sites 5. As illustrated in FIG. 1, IPunderlay network 4 includes provider edge (PE) routers 6A, 6A′, 6B and6B′ (collectively, “PEs 6”) that may establish EVPN 23 between sites 5Aand 5B. In this way, PEs 6 establish EVPN 23 to transport layer two (L2)communications for customer networks of sites 5 over an intermediatenetwork, e.g., IP underlay network 4, in a transparent manner, as if theintermediate network does not exist. In some examples, PEs 6 mayestablish EVPN 23 over IP underlay network 4 using the border gatewayprotocol (BGP). Although described with respect to EVPNs utilizing BGP,the techniques may be applied to other L2 VPNs and other routingprotocols.

In one example, PEs 6 may establish EVPN 23 as an EVPN overlay withVXLAN encapsulation over IP underlay network 4. In this example, variouscustomer networks provided within sites 5 may be virtually isolated ontodifferent EVPNs and VXLANs. For example, each of sites 5 may run VXLANsto transport L2 communications for its customer networks. As an example,PEs 6A, 6A′ may receive customer traffic from CE router 18A of site 5Aand forward the traffic over IP network 4 via EVPN 23 as the EVPNoverlay with VXLAN encapsulation, and may receive L2 communications fromremote PEs 6B, 6B′ via EVPN 23 as the EVPN overlay with VXLANencapsulation and forward the L2 communications to CE router 18A fortransport through site 5A over the VXLANs.

In other examples, PEs 6 may establish EVPN 23 as an EVPN overlay withNetwork Virtualization using Generic Routing Encapsulation (NVGRE) overIP underlay network 4, or may establish EVPN 23 as a Multi-ProtocolLabel Switching (MPLS) based EVPN over IP underlay network 4. Furtherexample structural and functional details of an EVPN as a VirtualNetwork Overlay (NVO) over an IP underlay network are described in “ANetwork Virtualization Overlay Solution using EVPN,”draft-sd-l2vpn-evpn-overlay-03.txt, Internet Engineering Task Force(IETF), Jun. 18, 2014, the entire contents of which are incorporatedherein by reference.

As shown in FIG. 1, each site 5A, 5B is multi-homed to IP underlaynetwork 4 for redundancy and load balancing. That is CE router 18A ofsite 5A is multi-homed to PE routers 6A, 6A′ using a multi-homedEthernet segment (ES) 10A in a single-active or anactive-active/all-active mode. Similarly, CE router 18B of site 5B ismulti-homed to PE routers 6B, 6B′ using a multi-homed ES 10B in asingle-active or an active-active/all-active mode. Each of themulti-homed ESs 10A, 10B may include a set of Ethernet links thatoperate as a link aggregation group (LAG). In other examples, CE routers18 may each be multi-homed to more than two PE routers of IP underlaynetwork 4.

As an example, when multi-homed ES 10A is operating in the all-activemode, traffic from CE router 18A may arrive at any of PE routers 6A, 6A′on multi-homed ES 10A and be forwarded accordingly via EVPN 23.Furthermore, traffic destined to CE router 18A may be received via EVPN23 at any of the PE routers 6A, 6A′ connected to multi-homed ES 10A.When forwarding L2 communications traversing EVPN 23, PE routers 6 learnL2 state information for the L2 customer networks within sites 5. The L2state information may include media access control (MAC) addressinginformation associated with the network devices and customer equipment(e.g., virtual machines) within sites 5 and the ports and/or pseudowiresof PE routers 6 through which the customer devices are reachable. The PErouters 6 typically store the MAC addressing information in L2 learningtables associated with each of their interfaces.

When multi-homed ES 10A is operating in the all-active mode, it ispossible that only a first PE router (e.g., PE 6A) on multi-homed ES 10Alearns a set of MAC addresses associated with traffic transmitted by CErouter 18A. A remote PE router (e.g., PE 6B) may then receive MAC routeadvertisements for the set of MAC addresses from only the first PErouter 6A. In this case, remote PE router 6B may not be able toeffectively load balance traffic destined for the set of MAC addressesacross all the PE routers 6A, 6A′ on the multi-homed ES 10A.

Aliasing refers to the ability of a PE router to signal that it canreach a given multi-homed ES in a given EVPN instance (EVI) even whenthe PE router has learned no MAC addresses from that EVI/ES. In theillustrated example of FIG. 1, if second PE router 6A′ supports aliasingfor multi-homed ES 10A, second PE router 6A′ may signal its aliasingcapability to, for example, remote PE router 6B. In this way, second PErouter 6A′ indicates to remote PE router 6B that second PE router 6A′can be used to reach multi-homed ES 10A, and in turn reach the set ofMAC addresses associated with CE router 18A, even though second PErouter 6A′ has not itself learned the set of MAC addresses overmulti-homed ES 10A.

Conventionally, each of the PE routers on a multi-homed ES sends aper-ES auto-discovery (AD) route advertisement to signal whether themulti-homed ES is operating in a single-active mode or anall-active/active-active mode. More specifically, the per-ES AD routemay be advertised with an Ethernet segment identifier (ESI) LabelExtended Community including a flag, e.g., a “Single-Active” flag, thatwhen set to 1 indicates that the multi-homed ES is in the single-activemode and when reset to 0 indicates that the multi-homed ES is theall-active mode. To signal aliasing capability, each of the PE routersalso sends a per-EVI AD route advertisement that indicates whether therespective PE router supports aliasing capability and includesadditional information needed by a remote PE to build an equal-costmulti-path (ECMP) next hop to the PE routers on the multi-homed ES.

In the case of MPLS based EVPN, each of the PE routers on a multi-homedES may advertise a per-ES AD route and a per-EVI AD route. In this way,when a remote PE router learns a MAC address over a non-reservedmulti-homed ES, the remote PE router may consider the multi-homed ES tobe reachable via a given PE router only if the remote PE router receivesfrom the given PE router a per-EVI AD route and a per-ES AD routeindicating that the multi-homed ES is in the all-active mode. In thiscase, the per-EVI AD route carries an MPLS aliasing label as theadditional information needed by the remote PE router to build an ECMPnext hop to the PE router on the multi-homed ES.

As an example, consider a CE1 that is dual-homed to two PEs (e.g., PE1and PE2) on a LAG interface (e.g., ES1), and is sending packets with asource MAC address MAC1 on a VLAN1, which is mapped to an EVI1. In theMPLS EVPN, if MAC1 is advertised only by PE1, a remote PE (e.g., PE3)considers MAC1 as being reachable via PE1 and PE2 only when PE1 and PE2each advertise a per-ES AD route for ES1 as well as a per-EVI AD routefor EVI1. An MPLS aliasing label included in the per-EVI AD route may beallocated for each of the advertising PE routers at differentgranularities (e.g., per-ES or per-EVI). On remote PE3, the MPLS labelin the MAC route advertised by PE1 is used to build an ECMP next hop toPE1 to reach MAC1 over ES1, while the aliasing label advertised in theper-EVI AD route from PE2 is used to build the ECMP next hop to PE2 toreach MAC1 over ES1.

In the case of an EVPN overlay with VXLAN encapsulation when the VNI forthe EVPN has a local scope, each of the PE routers on a multi-homed ESmay advertise a per-ES AD route and a per-EVI AD route. In this case,the per-EVI AD route carries the local VNI as the additional informationneeded by a remote PE router to build an ECMP next hop to the PE routeron the multi-homed ES. In the case of an EVPN overlay with VXLANencapsulation when the VNI for the EVPN has a global scope, each of thePE routers on a multi-homed ES may again advertise a per-ES AD route anda per-EVI AD route. In this case, however, the per-EVI AD route will notcarry any additional information needed by a remote PE router to buildan ECMP next hop to the PE router. This is because the remote PE routeruses the global VNI that is advertised with the MAC address by anotherPE router on the multi-homed ES to build the ECMP next hop to thealiasing PE router on the multi-homed ES.

Aliasing is an optional feature of the all-active mode for multi-homedESs. In order to use the aliasing feature, advertisement of the per-EVIAD route is needed if there is additional information (e.g., an MPLSaliasing label or a local scope VNI) that must be conveyed to the remotePE router to build the ECMP next hop correctly. In an EVPN overlay withVXLAN encapsulation using a globally unique VNI, the per-EVI AD route isonly used to indicate aliasing capability as no additional informationis needed to correctly build the ECMP next hop.

According to the techniques of this disclosure, the aliasing capabilitymay instead be signaled as part of the per-ES AD route advertisement. Inone example, the techniques of this disclosure extend the ESI LabelExtended Community advertised with the per-ES AD route to include analiasing bit that, when set, indicates that aliasing is supported by theadvertising PE router for a given multi-homed ES. In this way, for anEVPN overlay with VXLAN encapsulation using a globally unique VNI,advertisement of the per-EVI AD route is unnecessary, and the per-EVI ADroute advertisement may be suppressed.

In the example of FIG. 1, PE routers 6A, 6A′ on the multi-homed ES 10Aadvertise their aliasing capability using a per-ES AD routeadvertisement that includes the ESI Label Extended Community with thealiasing bit. In cases where multi-tenant data center 2 uses globallyunique VNIs, the remote PE router 6B, for example, may using the globalVNI to build an ECMP next hop to PE routers 6A, 6A′ that supportaliasing for multi-homed ES 10A. In this case, no additional informationis needed by remote PE 6B to build the ECMP next hop to reach the set ofMAC addresses learned over multi-homed ES 10A, and PE routers 6A, 6A′may suppress transmission of a per-EVI route advertisements.

FIG. 2 illustrates an example of an ESI Label Extended Community 50included with the per-ES AD route advertisement, in accordance with thetechniques of this disclosure. The ESI Label Extended Community 50includes a “Single-Active” flag, which may be included in flags field52, to indicate wither a given multi-homed ES is operating in asingle-active mode or an all-active mode. According to the techniques ofthis disclosure, aliasing capability may be signaled in the Reservedfield 53 of the ESI Label Extended Community 50 advertised with theper-ES AD route. As illustrated in FIG. 2, the least significant bit inthe Reserved field 53 is used for the purpose of signaling aliasingcapability with an A-bit 54. When A-bit 54 is set, i.e., equal to 1, itindicates that an advertising PE router supports the aliasing functionfor the multi-homed ES. When A-bit 54 is reset, i.e., equal to 0, itindicates that the advertising PE router does not support the aliasingfunction for the multi-homed ES. In the case of a EVPN overlay withVXLAN encapsulation using a globally unique VNI, a remote PE router mayuse the globally unique VNI label to correctly build an ECMP next hop tothe advertising PE router on the given multi-homed ES in order to reacha MAC address learned over the multi-homed ES.

Returning to the example of FIG. 1 in which EVPN 23 is a EVPN overlaywith VXLAN encapsulation using a globally unique VNI, CE 18A that isdual-homed to two PEs (i.e., PE 6A and PE 6A′) on a LAG interface (i.e.,ES 10A), and is sending packets with a source MAC address MAC1 on aVLAN1, which is mapped to an EVI1. In accordance with the techniques ofthis disclosure, if MAC1 associated with CE 18A is advertised only by PE6A in a MAC route advertisement, a remote PE (e.g., PE 6B) considersMAC1 as being reachable via PE 6A and PE 6A′ when PE 6B learns MAC1 fromPE 6A and receives a per-ES AD route for multi-homed ES 10A from PE 6A′with the “Single-Active” flag reset to indicate that multi-homed ES 10Ais in the all-active mode and the A-bit set to indicate that PE 6A′supports aliasing for multi-homed ES 10A.

At remote PE 6B, the globally unique VNI included in the MAC routeadvertised by PE 6A is used to build the ECMP next hop to PE 6A and PE6A′ to reach MAC1 over multi-homed ES 10A. Since the VNI is a globallyunique value, PE 6B may use the same VNI value to build the ECMP nexthop to reach multiple PE routers on multi-homed ES1 10A. In this way,remote PE 6B may use the global VNI from the MAC route advertised by PE6A to build the ECMP next hop to reach MAC1 over multi-homed ES 10A, andthen may add an additional next hop to PE 6A′ that supports aliasing formulti-homed ES 10A to the ECMP next hop to reach MAC1 over multi-homedES 10A. In other examples in which more than two PE routers areconnected to multi-homed ES 10A, PE 6B may use the globally unique VNIlabel to build an ECMP next hop to any of the PE routers that signaltheir support of aliasing for multi-homed ES 10A.

If PE 6A′ subsequently sends a per-ES AD route advertisement update withthe A-bit reset (i.e., equal to 0) to indicate that PE 6A′ no longersupports aliasing for multi-homed ES 10A, PE 6B may handle the routeupdate the same way as a per-EVI AD route withdrawal. In other words, PE6B may remove PE 6A′ from the ECMP next hop for the MACs learned overmulti-homed ES 10A, e.g., the ECMP next hop for MAC1. In the case of aEVPN overlay with VXLAN encapsulation using a globally unique VNI, if PE6B receives a per-EVI AD route from PE 6A′ after receiving the per-ES ADroute with the A-bit set from PE 6A′, it may be considerednon-operational (i.e., a no-op), as would a per-EVI AD route withdrawalreceived from PE 6A′. In the above case, PE 6B may discard the per-EVIAD route or per-EVI AD route withdrawal received from PE 6A′.

In general, this disclosure describes techniques that apply to EVPN 23as an EVPN overlay using VXLAN encapsulation when VNI has global scope.In this case, MPLS may not be running in IP underlay network 4, and theadvertisement of a per-EVI AD route may be suppressed by PE routers 6connected to multi-homed ESs 10. According to the techniques of thisdisclosure, aliasing capability is instead advertised through an A-bitin an ESI Label Extended Community included with a per-ES AD route. Thesuppressing of the per-EVI AD route for signaling aliasing capabilitydoes not apply to the case where EVPN 23 is an EVPN overlay using VXLANencapsulation when VNI has local scope, or where EVPN 23 is a MPLS basedEVPN running over IP underlay network 4. In these cases, PE routers 6 ofmulti-homed ESs 10 may send per-EVI AD route advertisements includingthe additional information, e.g., the local VNI or a MPLS aliasinglabel, needed to build the ECMP.

In order to support the aliasing function, one or more of the followingfour features may be used in any combination. First, the PE routers onthe multi-homed ES advertise their aliasing capability using per-ES ADroutes with the A-bit in the ESI Label Extended Community. This featureapplies to the EVPN overlay with VXLAN encapsulation. In some examples,this feature may also apply to the MPLS based EVPN.

Second, information for the remote PE to build the ECMP next hop to theMAC addresses learned over the multi-homed ES may be signaled to theremote PE. For the EVPN overlay with VXLAN encapsulation when VNI has aglobal scope, no additional information is needed. In this case, theremote PE can use the global VNI advertised in the MAC route by a firstPE on the multi-homed ES in order to build the ECMP next hop to multiplePEs on the multi-homed ES. For the MPLS EVPN or the EVPN overlay withVXLAN encapsulation when VNI has a local scope, additional information,such as the MPLS aliasing label or a local scope VNI, is needed to buildthe ECMP next hop. When additional information is needed to build theECMP next-hop, the additional information is still conveyed through aper-EVI AD route advertisement.

Third, by separating the aliasing capability signaling into a per-ES ADroute and any additional information needed to build the ECMP next hopinto a per-EVI AD route for the aliasing function, the per-EVI AD routecan be suppressed when no additional information is needed to build theECMP next hop. For example, in case of the EVPN overlay with VXLANencapsulation when VNI has a global scope, no additional information isneeded and only the per-ES AD route is advertised to signal aliasingcapability. Fourth, to make the described techniques backwardcompatible, the aliasing capability may be signaled using either theA-bit in the ESI Label Extended Community included in the per-ES ADroute, or an explicit advertisement of a per-EVI AD route.

The techniques of this disclosure may enable PE routers 6 to loadbalance L2 traffic to multi-homed CE routers 18 faster than inconventional techniques. In this way, the techniques may provide forless traffic loss due to the more efficient routing of L2 traffic.

FIG. 3 is a block diagram illustrating an example router 80 capable ofperforming the disclosed techniques. In general, router 80 may operatesubstantially similar to any of PEs 6 of FIG. 1. In the illustratedexample of FIG. 3, router 80 includes interface cards 88A-88N (“IFCs88”) that receive packets via incoming links 90A-90N (“incoming links90”) and send packets via outbound links 92A-92N (“outbound links 92”).IFCs 88 are typically coupled to links 90, 92 via a number of interfaceports. Router 80 also includes a control unit 82 that determines routesof received packets and forwards the packets accordingly via IFCs 88.

Control unit 82 may comprise a routing engine 84 and a forwarding engine86. Routing engine 84 operates as the control plane for router 80 andincludes an operating system that provides a multi-tasking operatingenvironment for execution of a number of concurrent processes. Routingengine 84 may implement one or more protocol 102 to execute routingprocesses. For example, routing protocols 102 may include Border GatewayProtocol (BGP) 103 for exchanging routing information with other routingdevices and for updating routing information 94. Routing information 94may describe a topology of the computer network in which router 80resides, and may also describe various routes within the network and theappropriate next hops for each route, i.e., the neighboring routingdevices along each of the routes. Routing engine 84 analyzes storedrouting information 94 and installs forwarding data structures intoforwarding information 106 of forwarding engine 86.

Routing engine 84 also includes an auto-discovery (AD) unit 100 that mayuse BGP 103 to both advertise AD routes to the neighboring routingdevices and discover or learn AD routes advertised by the neighboringrouting devices. In the example illustrated in FIG. 3, routinginformation 94 may include per-EVI routes 96 and per-ES routes 98. Whenrouter 80 is one of two or more PE routers on a multi-homed ES in agiven EVI, AD unit 100 may advertise per-EVI routes 98 and/or per-ESroutes 98. When router 80 is a remote router in a given EVI, AD unit 100may receive per-EVI routes 98 and/or per-ES routes 98 advertised by twoor more PE routers on a multi-homed ES in the given EVI.

Forwarding engine 86 operates as the data plane for router 80 forforwarding network traffic. In some examples, forwarding engine 86 maycomprise one or more packet forwarding engines (PFEs) (not shown) thatmay each comprise a central processing unit (CPU), memory and one ormore programmable packet-forwarding application-specific integratedcircuits (ASICs). Forwarding information 106 may associate, for example,network destinations with specific next hops and corresponding interfaceports of IFCs 88. Forwarding information 106 may be a radix treeprogrammed into dedicated forwarding chips, a series of tables, acomplex database, a link list, a radix tree, a database, a flat file, orvarious other data structures.

According to techniques of this disclosure, routing engine 84 may useBGP 103 to establish an EVPN as an NVO instance over an underlaynetwork, e.g., EVPN 23 over IP underlay network 4 from FIG. 1, between afirst site and a second site of a multi-tenant data center. The EVPN mayinclude two or more PE routers connected to a CE router on a multi-homedES in an all-active mode, and at least one remote PE router. Router 80may comprise any of the two or more PE routers on the multi-homed ES,e.g., PEs 6A, 6A′ from FIG. 1, or the at least one remote PE router,e.g., PE 6B from FIG. 1.

As a first PE router of the two or more PE routers on the multi-homedES, router 80 may receive a packet with a MAC address associated withthe CE router, and use BGP 103 to send, to the remote PE router, a MACroute advertisement including the MAC address of the CE router. As asecond PE router of the two or more PE routers on the multi-homed ES,router 80 may use AD unit 100 and BGP 103 to advertise, to the remote PErouter, a per-ES AD route 98 indicating whether router 80 supportsaliasing for the multi-homed ES. In some examples, the first PE routeradvertising the MAC route may also advertise a per-ES AD route 98indicating its aliasing capability. In other examples, each of the twoor more PE routers on the multi-homed ES may advertise a per-ES AD route98 indicating its aliasing capability.

As a remote PE router, router 80 may use BGP 103 to receive, from afirst PE router of the two or more PE routers on the multi-homed ES, aMAC route advertisement including a MAC address for the CE router. Inaddition, AD unit 100 of routing engine 84 may use BGP 103 to receive,from at least a second PE router of the two or more PE routers on themulti-homed ES, a per-ES AD route 98 indicating whether the second PErouter supports aliasing for the multi-homed ES. Based on the per-ES ADroute advertisement indicating that the second PE router supportsaliasing for the multi-homed ES, routing engine 84 may use routinginformation 94 to build an ECMP next hop in forwarding information 106to at least the first and second PE routers of the two or more PErouters on the multi-homed ES to reach the MAC address of the CE routerover the multi-homed ES. In other examples, router 80 may build the ECMPnext hop in forwarding information 106 to any of the two or more PErouters on the multi-homed ES that advertise support of the aliasingcapability in a per-ES AD route.

According to the techniques of this disclosure, one or more of theper-ES AD routes 98 may include an ESI Label Extended Community with analiasing bit, where the aliasing bit being set (e.g., equal to 1)indicates that the advertising PE router supports aliasing for themulti-homed ES, and the aliasing bit being reset (e.g., equal to 0)indicates that the advertising PE router does not support aliasing forthe multi-homed ES. The aliasing bit may comprises a least significantbit in a Reserved field in the ESI Label Extended Community advertisedwith the per-ES AD route, as illustrated in FIG. 2. The ESI LabelExtended Community also includes a flag indicating whether themulti-homed ES is in the all-active mode. Based on the flag indicatingthat the multi-homed ES is in the all-active mode and based on thealiasing bit being set, the ESI Label Extended Community advertised withthe per-ES AD route indicates to router 80 operating as the remote PErouter that the MAC address of the CE router is reachable via both thefirst PE router advertising the MAC route and the second PE routeradvertising aliasing capability for the multi-homed ES over which theMAC address was learned.

In an example of an EVPN overlay with VXLAN encapsulation when the VNIhas a global scope, router 80 operating as the remote PE router maybuild the ECMP next hop to at least the first and second PE routers onthe multi-homed ES using the globally unique VNI included in the MACroute advertised by the first PE router in order to reach the MACaddress of the CE router over the multi-homed ES. In this way, router 80operating as the remote PE router of the EVPN may build the ECMP nexthop by adding a next hop to the first PE router advertising the MACroute, and adding another next hop to each of the other PE routers onthe multi-homed ES advertising per-ES AD routes with the A-bit set inthe ESI Label Extended Community.

If, after receiving the per-ES AD route advertisement indicating thataliasing is supported for the multi-homed ES, router 80 operating as theremote PE router receives, from the second PE router on the multi-homedES, a per-ES AD route advertisement update with the aliasing bit resetto indicate that the second PE router no longer supports aliasing forthe multi-homed ES, router 80 may withdraw the second one of the two ormore PE routers from the ECMP next hop in forwarding information 106 forthe MAC address of the CE router.

In another example of an EVPN overlay with VXLAN encapsulation when theVNI has a local scope or a MPLS based EVPN, router 80 operating as oneof the two or more PE routers on the multi-homed ES may advertise itsaliasing capability using a per-ES AD route 98 including the ESI LabelExtended Community with the aliasing bit, and then advertise additionalinformation, e.g., the local VNI or a MPLS aliasing label, in a per-EVIAD route 96. In this example, since no global identifier is used, router80 operating as the remote PE router may build the ECMP next hop to anyof the PE routers that support aliasing for the multi-homed ES usinglocal VNI or the MPLS aliasing label included in the per-EVI AD routes96 in order to reach the MAC address of the CE router over themulti-homed ES.

In yet another example of an EVPN overlay with VXLAN encapsulation whenthe VNI has a local scope or as a MPLS based EVPN, in order to be fullybackward compatible, router 80 operating as one of the two or more PErouters on the multi-homed ES may advertise its aliasing capability andthe additional information needed to build the ECMP next hop using aper-EVI AD route 96.

The architecture of router 80 illustrated in FIG. 3 is shown forexemplary purposes only. The techniques of this disclosure are notlimited to this architecture. In other examples, router 80 may beconfigured in a variety of ways. In one example, some of thefunctionally of control unit 82 may be distributed within IFCs 88 or aplurality of packet forwarding engines (PFEs) (not shown). Control unit82 may be implemented solely in software, or hardware, or may beimplemented as a combination of software, hardware, or firmware. Forexample, control unit 82 may include one or more processors whichexecute software instructions. In that case, the various softwaremodules of control unit 82 may comprise executable instructions storedon a computer-readable medium, such as computer memory or hard disk.

FIG. 4 is a flowchart illustrating an example operation of PE routers ona multi-homed ES signaling aliasing capability to a remote PE in amulti-tenant data center using EVPNs. The operation of FIG. 4 isdescribed with respect to first PE 6A and second PE 6A′ on multi-homedES 10A, and remote PE 6B from FIG. 1. Although the operation of FIG. 4is described as being performed by only two PE routers on a multi-homedES, a similar operation may be performed by more than two PE routers ona multi-homed ES. In other examples, the operation of FIG. 4 may beperformed by PE 6B and PE 6B′ on multi-homed ES 10B from FIG. 1, or maybe performed by router 80 of FIG. 3 operating as one of the PE routerson a multi-homed ES.

First PE 6A and second PE 6A′ may communicate with one or more of remotePE 6B and remote PE 6B′ to establish EVPN 23 as an EVPN overlay withVXLAN encapsulation over IP network 4 in multi-tenant data center 2 thatuses a global VNI (110). First PE 6A and second PE 6A′ connect to CE 18Aof first site 5A of multi-tenant data center 2 via multi-homed ES1 10Ain an all-active mode.

According to the techniques of this disclosure, at least second PE 6A′sends a per-ES AD route advertisement indicating whether second PE 6A′supports aliasing for multi-homed ES 10A to, e.g., remote PE 6B (112).The per-ES AD route advertisement sent by second PE 6A′ includes an ESILabel Extended Community with an aliasing bit (i.e., an A-bit). When theA-bit is set (e.g., equal to 1), it indicates that second PE 6A′supports aliasing for the multi-homed ES 10A, and when the A-bit isreset (e.g., equal to 0), it indicates that second PE 6A′ does notsupport aliasing for the multi-homed ES 10A. In the example where theA-bit is set, second PE 6A′ indicates to remote PE 6B that second PE 6A′can be used to reach multi-homed ES 10A, and in turn reach MAC addressesover multi-homed ES 10A, even though second PE 6A′ has not itselflearned the MAC addresses over multi-homed ES 10A.

Although this disclosure primary describes the per-ES AD routeadvertisement including the ESI Label Extended Community with thealiasing bit being sent only by second PE 6A′, the techniques of thisdisclosure are not so limited. In some examples, each of first PE 6A andsecond PE 6A′ may send a per-ES AD route advertisement including the ESILabel Extended Community with the aliasing bit to indicate whether therespective one of first PE 6A and second PE 6A′ supports aliasing formulti-homed ES 10A. In other examples in which more than two PE routersare included in a multi-homed ES, each of the two or more PE routers onthe multi-homed ES may send a per-ES AD route advertisement includingthe ESI Label Extended Community with the aliasing bit to indicatewhether the respective PE router supports aliasing for the multi-homedES.

In the example of EVPN 23 as an EVPN overlay with VXLAN encapsulationwhen the VNI has a global scope, second PE 6A′ may signal its aliasingcapability to remote PE 6B using only the per-ES AD route advertisementincluding the ESI Label Extended Community with the aliasing bit, andsuppress transmission of a per-EVI AD route advertisement (114). In thisexample, the additional information typically included in the per-EVI ADroute advertisement, e.g., a local VNI or MPLS aliasing label, is notneeded by remote PE 6B to build an ECMP next hop to reach MAC addressesover multi-homed ES 10A. Instead, remote PE 6B may use the global VNIincluded in a MAC route advertisement from another PE router, e.g.,first PE 6A, on multi-homed ES 10A to build an ECMP next hop to bothfirst PE 6A and second PE 6A′ to reach the MAC addresses overmulti-homed ES 10A.

After multi-homed ES 10A is configured, first PE 6A on multi-homed ES10A receives a packet from CE 18A that includes a MAC address of CE 18A(116). In response to receiving the packet, first PE 6A sends a MACroute advertisement including the MAC address of CE 18A and the globalVNI to, e.g., remote PE 6B (118). Either first PE 6A or second PE 6A′may receive data packets destined for the MAC address of the CE router(120). In this case, the data packets may be received from remote PE 6Baccording to the ECMP next hop built using the global VNI. In otherexamples in which more than two PE routers are included in a multi-homedES, any of the two or more PE routers that indicated support of thealiasing capability for the multi-homed ES may receive data packetsdestined for the MAC addresses learned over the multi-homed ES.

In the example of EVPN 23 as an EVPN overlay with VXLAN encapsulationwhen the VNI has a local scope or as a MPLS based EVPN, second PE 6A′may still signal its aliasing capability to remote PE 6B using theper-ES AD route advertisement including the ESI Label Extended Communitywith the aliasing bit, and then send additional information, e.g., thelocal VNI or a MPLS aliasing label, to remote PE 6B in a per-EVI ADroute advertisement. In this example, since no global identifier isused, the additional information is needed by remote PE 6B to build anECMP next hop to both first PE 6A and second PE 6A′ to reach the MACaddress of CE 18A over multi-homed ES 10A. In yet another example ofEVPN 23 as an EVPN overlay with VXLAN encapsulation when the VNI has alocal scope or as a MPLS based EVPN, in order to be fully backwardcompatible, second PE 6A′ may signal its aliasing capability and theadditional information needed to build the ECMP next hop to remote PE 6Busing a per-EVI AD route advertisement.

FIG. 5 is a flowchart illustrating an example operation of a remote PErouter receiving aliasing capability signaling from PE routers on amulti-homed ES in a multi-tenant data center using EVPNs. The operationof FIG. 5 is described with respect to remote PE 6B, and first PE 6A andsecond PE 6A′ on multi-homed ES 10A from FIG. 1. Although the operationof FIG. 4 is described as being performed by a remote PE with respect toonly two PE routers on a multi-homed ES, a similar operation may beperformed by a remote PE with respect to more than two PE routers on amulti-homed ES. In other examples, the operation of FIG. 5 may beperformed by any of PE 6A, PE 6A′ or PE 6B′ from FIG. 1, or may beperformed by router 80 of FIG. 3 operating as a remote PE routerincluded in an EVPN.

Remote PE 6B may communicate with one or more of remote PE 6B′, first PE6A and second PE 6A′ to establish EVPN 23 as an EVPN overlay with VXLANencapsulation over IP network 4 in multi-tenant data center 2 that usesa global VNI (130). Remote PE 6B connects to first PE 6A and second PE6A′ via EVPN 23, and first PE 6A and second PE 6A′ connect to CE 18A offirst site 5A of multi-tenant data center 2 via multi-homed ES1 10A inan all-active mode.

According to the techniques of this disclosure, remote PE 6B receives aper-ES AD route advertisement from, e.g., second PE 6A′, indicatingwhether second PE 6A′ supports aliasing for multi-homed ES 10A (132).The per-ES AD route advertisement received from second PE 6A′ includesan ESI Label Extended Community with an aliasing bit (i.e., an A-bit).When the A-bit is set (e.g., equal to 1), it indicates that second PE6A′ supports aliasing for the multi-homed ES 10A, and when the A-bit isreset (e.g., equal to 0), it indicates that second PE 6A′ does notsupport aliasing for the multi-homed ES 10A. In the example where theA-bit is set, remote PE 6B learns that second PE 6A′ can be used toreach multi-homed ES 10A, and in turn reach MAC addresses overmulti-homed ES 10A, even though remote PE 6B has not received a MACroute advertisement for the MAC addresses from second PE 6A′.

Although this disclosure primary describes the per-ES AD routeadvertisement including the ESI Label Extended Community with thealiasing bit being received by remote PE 6B from only second PE 6A′, thetechniques of this disclosure are not so limited. In some examples,remote PE 6B may receive a per-ES AD route advertisement including theESI Label Extended Community with the aliasing bit from each of first PE6A and second PE 6A′ indicating whether the respective one of first PE6A and second PE 6A′ supports aliasing for multi-homed ES 10A. In otherexamples in which more than two PE routers are included in a multi-homedES, remote PE 6B may receive a per-ES AD route advertisement includingthe ESI Label Extended Community with the aliasing bit from each of thetwo or more PE routers on the multi-homed ES indicating whether therespective PE router supports aliasing for the multi-homed ES.

In the example of EVPN 23 as an EVPN overlay with VXLAN encapsulationwhen the VNI has a global scope, remote PE 6B may learn the aliasingcapability of second PE 6A′ based on only the per-ES AD routeadvertisement including the ESI Label Extended Community with thealiasing bit received from second PE 6A′. In this example, additionalinformation typically included in per-EVI AD route advertisements, e.g.,a local VNI or MPLS aliasing label, is not needed by remote PE 6B tobuild an ECMP next hop to reach the MAC addresses over multi-homed ES10A. Instead, remote PE 6B may use the global VNI included in a MACroute advertisement from another PE router, e.g., first PE 6A, onmulti-homed ES 10A to build an ECMP next hop for the MAC addresses.

After the multi-homed ES 10A is configured, remote PE 6B receives a MACroute advertisement from, e.g., first PE 6A on multi-homed ES 10A thatincluding a MAC address of CE 18A and the global VNI (134). If the A-bitis set in the per-ES AD route advertisement received from second PE 6A′indicating that second PE 6A′ supports aliasing for multi-homed ES 10A(YES branch of 136), remote PE 6B builds an ECMP next hop to first PE 6Aand second PE 6A′ on multi-homed ES 10A using the global VNI to reachthe MAC address of CE 18A over multi-homed ES 10A (138). Remote PE 6Bmay then send data packets destined for the MAC address of the CE routerto either first PE 6A or second PE 6A′ according to the ECMP next hopfor the MAC address of the CE router (142). If remote PE 6B subsequentlyreceives from second PE 6A′ a per-ES AD route advertisement update withthe A-bit reset indicating that second PE 6A′ no longer supportsaliasing for multi-homed ES 10A, remote PE 6B may withdraw second PE 6A′from the ECMP next hop for the MAC address of CE 18A. In other examplesin which more than two PE routers are included in a multi-homed ES,remote PE 6B may build an ECMP next hop to any of the two or more PErouters that indicated support of the aliasing capability for themulti-homed ES using the global VNI to reach a MAC address learned overthe multi-homed ES.

If the A-bit is reset in the per-ES AD route advertisement received fromsecond PE 6A′ indicating that second PE 6A′ does not support aliasingfor multi-homed ES 10A (NO branch of 136), remote PE 6B builds a nexthop only to first PE 6A based on the MAC route advertisement from firstPE 6A to reach the MAC address of the CE router over multi-homed ES 10A(140). Remote PE 6B may then send data packets destined for the MACaddress of the CE router to only first PE router 6A, i.e., the sender ofthe MAC route advertisement, according to the next hop for the MACaddress of the CE router (142).

In the example of EVPN 23 as an EVPN overlay with VXLAN encapsulationwhen the VNI has a local scope or as a MPLS based EVPN, remote PE 6B maystill learn the aliasing capability of second PE 6A′ based on the per-ESAD route advertisement including the ESI Label Extended Community withthe aliasing bit received from second PE 6A′, and then learn additionalinformation, e.g., the local VNI or a MPLS aliasing label, based on aper-EVI AD route advertisement also received from second PE 6A′. In thisexample, since no global identifier is used, remote PE 6B builds an ECMPnext hop to first PE 6A and second PE 6A′ on multi-homed ES 10A usingeither the local VNI or the MPLS aliasing label to reach the MAC addressof CE 18A over multi-homed ES 10A. In yet another example of EVPN 23 asan EVPN overlay with VXLAN encapsulation when the VNI has a local scopeor as a MPLS based EVPN, in order to be fully backward compatible,remote PE 6B may learn the aliasing capability of second PE 6A′ and theadditional information needed to build the ECMP next hop based on aper-EVI AD route advertisement received from second PE 6A′.

Although primary described above with respect to EVPNs utilizing BGP,and specifically to EVPN overlays with VXLAN encapsulation over IPunderlay networks when VNI has a global scope, the techniques of thisdisclosure may be applied to other L2 VPNs and other routing protocols.For example, in a multi-tenant data center, two or more PE routers maybe connected to a CE router by a multi-homed L2 network segment, e.g., amulti-homed ES, in an all-active mode. According to the techniques ofthis disclosure, the PE routers on the multi-homed L2 segment utilize anenhanced routing protocol that allows the PE routers to signal aliasingcapability on an L2 segment basis (e.g., per-ES). In this way, each ofthe PE routers on the multi-homed L2 segment that did not learn a set ofMAC addresses associated with the CE router may nevertheless signal thatit can reach the given set of MAC addresses over the multi-homed L2segment. In addition, in some examples in which a global VPN identifieris used, each of the PE routers on the multi-homed L2 segment maysuppress transmission of an additional route advertisement on a per-VPNbasis (e.g., per-EVI).

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Various featuresdescribed as modules, units or components may be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices or other hardware devices. In some cases, various featuresof electronic circuitry may be implemented as one or more integratedcircuit devices, such as an integrated circuit chip or chipset.

If implemented in hardware, this disclosure may be directed to anapparatus such a processor or an integrated circuit device, such as anintegrated circuit chip or chipset. Alternatively or additionally, ifimplemented in software or firmware, the techniques may be realized atleast in part by a computer-readable data storage medium comprisinginstructions that, when executed, cause a processor to perform one ormore of the methods described above. For example, the computer-readabledata storage medium may store such instructions for execution by aprocessor.

A computer-readable medium may form part of a computer program product,which may include packaging materials. A computer-readable medium maycomprise a computer data storage medium such as random access memory(RAM), read-only memory (ROM), non-volatile random access memory(NVRAM), electrically erasable programmable read-only memory (EEPROM),Flash memory, magnetic or optical data storage media, and the like. Insome examples, an article of manufacture may comprise one or morecomputer-readable storage media.

In some examples, the computer-readable storage media may comprisenon-transitory media. The term “non-transitory” may indicate that thestorage medium is not embodied in a carrier wave or a propagated signal.In certain examples, a non-transitory storage medium may store data thatcan, over time, change (e.g., in RAM or cache).

The code or instructions may be software and/or firmware executed byprocessing circuitry including one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application-specific integrated circuits (ASICs), field-programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, functionality described in this disclosure may be providedwithin software modules or hardware modules.

Various embodiments have been described. These and other embodiments arewithin the scope of the following examples.

What is claimed is:
 1. A method comprising: establishing, between afirst site and a second site of a multi-tenant data center, an Ethernetvirtual private network (EVPN) including two or more provider edge (PE)routers connected to a customer edge (CE) router of the first site on amulti-homed Ethernet segment (ES) in an all-active mode, and at leastone remote PE router; receiving, by a first PE router of the two or morePE routers on the multi-homed ES from the CE router, a packet with amedia access control (MAC) address associated with the CE router;sending, by the first PE router to the at least one remote PE router, aMAC route advertisement including the MAC address associated with the CErouter; and sending, by at least a second PE router of the two or morePE routers on the multi-homed ES to the at least one remote PE router, aper-ES auto-discovery (AD) route advertisement indicating whether thesecond PE router supports aliasing for the multi-homed ES.
 2. The methodof claim 1, wherein the EVPN comprises an EVPN overlay with VirtualExtensible Local Area Network (VXLAN) encapsulation over an InternetProtocol (IP) underlay network that uses a global Virtual NetworkIdentifier (VNI), and wherein sending the MAC route advertisementcomprises sending, by the first PE router to the remote PE router, theglobal VNI included in the MAC route advertisement.
 3. The method ofclaim 2, further comprising suppressing, by the second PE router,transmission of a per-EVPN instance (EVI) AD route advertisement to theremote PE router.
 4. The method of claim 2, further comprising, based onthe per-ES AD route advertisement indicating that the second PE routersupports aliasing for the multi-homed ES, receiving, by the second PErouter from the remote PE router according to an Equal Cost Multipath(ECMP) next hop built using the global VNI, data packets destined forthe MAC address associated with the CE router.
 5. The method of claim 1,wherein the EVPN comprises one of an EVPN overlay with VirtualExtensible Local Area Network (VXLAN) encapsulation over an InternetProtocol (IP) underlay network that uses local Virtual NetworkIdentifiers (VNIs) or a Multi-Protocol Label Switching (MPLS) basedEVPN, the method further comprising: based on the second PE routersupporting aliasing for the multi-homed ES, sending, by the second PErouter to the remote PE router, a per-EVPN instance (EVI) AD routeadvertisement indicating one of the local VNI or a MPLS aliasing label;and receiving, by the second PE router from the remote PE routeraccording to an Equal Cost Multipath (ECMP) next hop built using the oneof the local VNI or the MPLS aliasing label, data packets destined forthe MAC address associated with the CE router.
 6. The method of claim 1,wherein the per-ES AD route advertisement sent by the second PE routerincludes an Ethernet Segment Identifier (ESI) Label Extended Communitywith an aliasing bit, wherein the aliasing bit being set indicates thatthe second PE router supports aliasing for the multi-homed ES, and thealiasing bit being reset indicates that the second PE router does notsupport aliasing for the multi-homed ES.
 7. The method of claim 1,wherein sending the per-ES AD route advertisement comprises sending, byat least the first PE router and the second PE router to the remote PErouter, a per-ES AD route advertisement indicating whether therespective PE router supports aliasing for the multi-homed ES.
 8. Themethod of claim 1, wherein sending the per-ES AD route advertisementcomprises sending, by each of the two or more PE routers on themulti-homed ES to the remote PE router, a per-ES AD route advertisementindicating whether the respective PE router supports aliasing for themulti-homed ES.
 9. A system comprising: two or more provider edge (PE)routers included in an Ethernet virtual private network (EVPN)established between a first site and a second site of a multi-tenantdata center, the two or more PE routers connected to a customer edge(CE) router of the first site on a multi-homed Ethernet segment (ES) inan all-active mode; a first PE router of the two or more PE routers onthe multi-homed ES configured to receive, from the CE router, a packetwith a media access control (MAC) address associated with the CE router,and send, to at least one remote PE router included in the EVPN, a MACroute advertisement including the MAC address associated with the CErouter; and a second PE router of the two or more PE routers on themulti-homed ES configured to send, to the at least one remote PE router,a per-ES auto-discovery (AD) route advertisement indicating whether thesecond PE router supports aliasing for the multi-homed ES.
 10. Thesystem of claim 9, wherein the EVPN comprises an EVPN overlay withVirtual Extensible Local Area Network (VXLAN) encapsulation over anInternet Protocol (IP) underlay network that uses a global VirtualNetwork Identifier (VNI), and wherein the first PE router is configuredto send, to the remote PE router, the global VNI included in the MACroute advertisement.
 11. The system of claim 10, wherein the second PErouter is configured to suppress transmission of a per-EVPN instance(EVI) AD route advertisement to the remote PE router.
 12. The system ofclaim 10, wherein the remote PE router is configured to, based on theper-ES AD route advertisement indicating that the second PE routersupports aliasing for the multi-homed ES, receive, from the remote PErouter according to an Equal Cost Multipath (ECMP) next hop built usingthe global VNI, data packets destined for the MAC address associatedwith the CE router.
 13. The system of claim 9, wherein the EVPNcomprises one of an EVPN overlay with Virtual Extensible Local AreaNetwork (VXLAN) encapsulation over an Internet Protocol (IP) underlaynetwork that uses local Virtual Network Identifiers (VNIs) or aMulti-Protocol Label Switching (MPLS) based EVPN, wherein the second PEis configured to: based on the second PE router supporting aliasing forthe multi-homed ES, send, to the remote PE router, a per-EVPN instance(EVI) AD route advertisement indicating one of the local VNI or a MPLSaliasing label; and receive, from the remote PE router according to anEqual Cost Multipath (ECMP) next hop built using the one of the localVNI or the MPLS aliasing label, data packets destined for the MACaddress associated with the CE router.
 14. The system of claim 9,wherein the per-ES AD route advertisement sent by the second PE routerincludes an Ethernet Segment Identifier (ESI) Label Extended Communitywith an aliasing bit, wherein the aliasing bit being set indicates thatthe second PE router supports aliasing for the multi-homed ES, and thealiasing bit being reset indicates that the second PE router does notsupport aliasing for the multi-homed ES.
 15. The system of claim 9,wherein each of the first PE router and the second PE router areconfigured to send, to the remote PE router, a per-ES AD routeadvertisement indicating whether the respective PE router supportsaliasing for the multi-homed ES.
 16. The system of claim 9, wherein eachof the two or more PE routers on the multi-homed ES are configured tosend, to the remote PE router, a per-ES AD route advertisementindicating whether the respective PE router supports aliasing for themulti-homed ES.
 17. A method comprising: establishing, between a firstsite and a second site of a multi-tenant data center, an Ethernetvirtual private network (EVPN) including two or more provider edge (PE)routers connected to a customer edge (CE) router of the first site on amulti-homed Ethernet segment (ES) in an all-active mode, and at leastone remote PE router; receiving, by the remote PE router from a first PErouter of the two or more PE routers on the multi-homed ES, a mediaaccess control (MAC) route advertisement including a MAC addressassociated with the CE router; receiving, by the remote PE router fromat least a second PE router of the two or more PE routers on themulti-homed ES, a per-ES auto-discovery (AD) route advertisementindicating whether the second PE router supports aliasing for themulti-homed ES; and based on the per-ES AD route advertisementindicating that the second PE router supports aliasing for themulti-homed ES, building, by the remote PE router, an equal-costmulti-path (ECMP) next hop to at least the first and second PE routerson the multi-homed ES to reach the MAC address associated with the CErouter over the multi-homed ES.
 18. The method of claim 17, wherein theEVPN comprises an EVPN overlay with Virtual Extensible Local AreaNetwork (VXLAN) encapsulation over an Internet Protocol (IP) underlaynetwork that uses a global Virtual Network Identifier (VNI), the methodfurther comprising: receiving the global VNI included in the MAC routeadvertisement from the first PE router; and building the ECMP next hopto at least the first and second PE routers on the multi-homed ES usingthe global VNI.
 19. The method of claim 17, wherein the EVPN comprisesone of an EVPN overlay with Virtual Extensible Local Area Network(VXLAN) encapsulation over an Internet Protocol (IP) underlay networkthat uses local Virtual Network Identifiers (VNIs) or a Multi-ProtocolLabel Switching (MPLS) based EVPN, the method further comprising:receiving, by the remote PE router from the second PE router, a per-EVPNinstance (EVI) AD route advertisement indicating one of the local VNI oran MPLS aliasing label; and building the ECMP next hop to at least thefirst and second PE routers on the multi-homed ES using the one of thelocal VNI or the MPLS aliasing label.
 20. The method of claim 17,wherein the per-ES AD route advertisement from the second PE routerincludes an Ethernet Segment Identifier (ESI) Label Extended Communitywith an aliasing bit, wherein the aliasing bit being set indicates thatthe second PE router supports aliasing for the multi-homed ES, and thealiasing bit being reset indicates that the second PE router does notsupport aliasing for the multi-homed ES.
 21. The method of claim 17,wherein receiving the per-ES AD route advertisement comprises receiving,by the remote PE router from each of at least the first PE router andthe second PE router, a per-ES AD route advertisement indicating whetherthe respective PE router supports aliasing for the multi-homed ES. 22.The method of claim 17, further comprising: receiving, by the remote PErouter from the second PE router, a per-ES AD route advertisement updateindicating that the second PE router does not support aliasing for themulti-homed ES; and withdrawing the second PE router from the ECMP nexthop for the MAC address associated with the CE router.
 23. A routercomprising: a routing engine configured to: establish an Ethernetvirtual private network (EVPN) between a first site and a second site ofa multi-tenant data center, the EVPN including two or more provider edge(PE) routers connected to a customer edge (CE) router of the first siteon a multi-homed Ethernet segment (ES) in an all-active mode, whereinthe router is a remote PE router included in the EVPN, receive, from afirst PE router of the two or more PE routers on the multi-homed ES, amedia access control (MAC) route advertisement including a MAC addressassociated with the CE router, receive, from at least a second PE routerof the two or more PE routers on the multi-homed ES, a per-ESauto-discovery (AD) route advertisement indicating whether the second PErouter supports aliasing for the multi-homed ES, and based on the per-ESAD route advertisement indicating that the second PE supports aliasingfor the multi-homed ES, build an equal-cost multi-path (ECMP) next hopto at least the first and second PE routers on the multi-homed ES toreach the MAC address associated with the CE router over the multi-homedES; and a forwarding engine configured to forward data packets destinedfor the MAC address associated with the CE router according to the ECMPnext hop.
 24. The router of claim 23, wherein the EVPN comprises an EVPNoverlay with Virtual Extensible Local Area Network (VXLAN) encapsulationover an Internet Protocol (IP) underlay network that uses a globalVirtual Network Identifier (VNI), and wherein the routing engine isfurther configured to: receive the global VNI included in the MAC routeadvertisement from the first PE router; and build the ECMP next hop toat least the first and second PE routers on the multi-homed ES using theglobal VNI.
 25. The router of claim 23, wherein the EVPN comprises oneof an EVPN overlay with Virtual Extensible Local Area Network (VXLAN)encapsulation over an Internet Protocol (IP) underlay network that useslocal Virtual Network Identifiers (VNIs) or a Multi-Protocol LabelSwitching (MPLS) based EVPN, and wherein the routing engine is furtherconfigured to: receive, from the second PE router, a per-EVPN instance(EVI) AD route advertisement indicating one of the local VNI or an MPLSaliasing label; and build the ECMP next hop to at least the first andsecond PE routers on the multi-homed ES using the one of the local VNIor the MPLS aliasing label.
 26. The router of claim 23, wherein theper-ES AD route advertisement from the second PE router includes anEthernet Segment Identifier (ESI) Label Extended Community with analiasing bit, wherein the aliasing bit being set indicates that thesecond PE router supports aliasing for the multi-homed ES, and thealiasing bit being reset indicates that the second PE router does notsupport aliasing for the multi-homed ES.
 27. The router of claim 23,wherein the routing engine is further configured to receive, from eachof at least the first PE router and the second PE router, a per-ES ADroute advertisement indicating whether the respective PE router supportsaliasing for the multi-homed ES.
 28. The router of claim 23, wherein therouting engine is further configured to: receive, from the second PErouter, a per-ES AD route advertisement update indicating that thesecond PE router does not support aliasing for the multi-homed ES; andwithdraw the second PE router from the ECMP next hop for the MAC addressassociated with the CE router.
 29. A method comprising: establishing,between a first site and a second site of a multi-tenant data center, alayer two virtual private network (L2 VPN) between two or more provideredge (PE) routers and at least one remote PE router, wherein the two ormore PE routers are connected to a customer edge (CE) router of thefirst site by a multi-homed L2 network segment associated with aparticular customer, and wherein the two or more PE routers areconfigured to operate in an all-active mode in which all of the PErouters forward L2 traffic from the at least one remote PE to the CErouter over the multi-homed L2 network segment; receiving, by a first PErouter of the two or more PE routers and from the CE router, a packetwith an L2 address associated with the CE router; sending, by the firstPE router to the at least one remote PE router, a route advertisementincluding the L2 address associated with the CE router; sending, by atleast a second PE router of the two or more PE routers to the at leastone remote PE router using a routing protocol, an auto-discovery (AD)route advertisement associated with the multi-homed L2 network segmentindicating whether the second PE router supports aliasing for themulti-homed L2 network segment to reach the L2 address associated withthe CE router without having learned the L2 address over the multi-homedL2 network segment; and when the L2 VPN uses a global identifier,suppressing, by the second PE router, transmission of another AD routeadvertisement associated with a VPN instance of the L2 VPN.
 30. Themethod of claim 29, wherein the L2 VPN comprises an Ethernet virtualprivate network (EVPN) and the multi-homed L2 network segment comprisesa multi-homed Ethernet segment (ES), and wherein the AD routeadvertisement associated with the multi-homed L2 network segmentcomprises a per-ES auto-discovery (AD) route advertisement that includesan Ethernet Segment Identifier (ESI) Label Extended Community with analiasing bit, wherein the aliasing bit being set indicates that thesecond PE router supports aliasing for the multi-homed ES, and thealiasing bit being reset indicates that the second PE router does notsupport aliasing for the multi-homed ES.